The present invention relates to an ion working machine for performing ion implantation, ion beam sputtering, surface reforming with ions, and so on, and particularly relates to a microwave ion source suitable for use in an apparatus which requires ions of an element of high reactivity such as oxygen, fluorine, etc.
Conventionally, there have been three kinds of methods for transmitting microwave energy as follows:
(1) Transmission through a rectangular waveguide;
(2) Transmission through a hollow cylindrical waveguide; and
(3) Transmission through between outer and inner conductors of a coaxial waveguide.
The above method (3) using a coaxial waveguide has been widely used because of its various advantages as follows:
(a) The microwave energy can be guided even if a microwave ion source is made small in size;
(b) The microwave ion source can be made small in size with the impedance unchanged; and
(c) Such a coaxial cable as generally sold can be used as the coaxial waveguide.
In such a conventional microwave ion source having a coaxial structure, as disclosed in JP-A-59-96632, a permanent magnet for generating a magnetic field is arranged to surround a plasma chamber (discharge chamber) and an ion extracting electrode supplied with a voltage different from that applied to the plasma chamber is formed of a high magnetic permeability material. Further, a coaxial line made of metal of high electrical conductivity for supplying the plasma chamber with microwave energy is exposed in the plasma chamber.
Accordingly, the above prior art has problems in the three points as follows.
(1) Since there exists an intense magnetic field of an order of 0.1 T in the space exerted with an electric field between an acceleration electrode and a deceleration electrode (ion extraction electrode), it is impossible to make the discharge-resistant voltage across the acceleration and deceleration electrodes high and therefore this technique is not suitable for large-current extraction.
(2) Since a permanent magnet is arranged to surround a plasma chamber, it is difficult to two-dimensionally enlarge the plasma chamber in its section.
(3) Since a microwave coaxial line is exposed in a plasma chamber, metal elements such as copper, titanium, etc., sputtered from the coaxial line mix with plasma generated in the plasma chamber to thereby lower the purity of the plasma. Further, the metal elements may attach onto the surface of a dielectric insulator interposed between the inner and outer conductors of the coaxial line to thereby make it impossible to supply the plasma chamber with a microwave.